It’s not part of the Fermi paradox. It’s just one proposed form of technology that seems very plausible to us to see.
And in general, I think it’s the wrong framing to see the Fermi paradox as making a positive claim.
I know a lot of scientists and writers see it that way (even one of my favorite science channels, the science asylum sees it that way), but I think they’re wrong.
Because, what happens is, they will say that the Fermi paradox is: “Based on several assumptions, we should see lots of ETIs.” They’ll then question those assumptions, and conclude that the Fermi paradox is “solved”. But what have we solved?
The better framing is simply: “Based only on what we know of physics, biology and cosmology today, we know of no reason why the sky isn’t teeming with ETIs”. This makes it clearer that it is not about making a positive claim, it’s about highlighting the significant, profound, unknowns.
What I am saying by “close” to making replicating drones, is “within the next couple millenia”.
Remember, we’re talking about a universe that is billions of years old. Any species that is ahead of us technologically is likely to be millions of years ahead of us, just because of how unlikely it is that their development would match ours any more precisely than that.
It’s barely more than two centuries ago that our fastest transportation was sitting on a horse. Now we can land probes on asteroids.
Let me be very clear: I am not saying “millions of years, therefore magic”. There will still be physically impossible things, and problems that they are unable to solve.
But, I think it’s pretty safe to say that the set of problems that we consider “stupidly difficult engineering challenges” will belong to their set of “easy” problems. Solved in their ancient history. Their “hard” problems will be things we don’t even know about yet.
The word *may is doing a lot of heavy lifting here. We don’t even know how to make fully aelf-replicating machinea right here on Earth, even providing them with refined materials. Making something that can travel to another star system then roam among the planets nd asteroids prospecting for materials, harvesting them, and assembling them into a copy of itself is a feat so far beyond what we can even imagine doing that it might as well be magic. If you want a ‘great filter’, I’d say the likeliest one is that mo civilization has ever gotten to the point where they could mle sirpch a thing, lr if they did, long before they got there they lost the desire to domit because their tech is so advanced that going to other stars for resources is a quaint concept.
Let me give you an example: In the 1800’s, Big cannons were all the rage. Futurists of the time assumed that if we ever traveled into space, we’d do it by making huge cannons and blasting stuff into space. The first science fictiion kovie depicted a trip like that.
At the time, we didn’t have the engineering or metallurgy to make sure a large cannon, so futurists could easily have had the same conversation we’re having: “One day science will figure out how to make giant cannons, then we’ll explore space!” Maybe their visions of advanced civilizatiins were ones festooned with giant cannons. And indeed, we are at the level where an orbital cannon is not completely outrageous as an idea, but by the time we got there we had much better ways to launch people into space and it’s safe to say that we will never launch stuff into space that way, even if we could.
So maybe by the time a civilization gets so advanced that it could launch self-replicating probes, the very idea will be seen as silly. Or maybe the implementation is just so freaking hard that there are thousands of civilizations in the galaxy but none have managed to send anything but simple probes beyond their star system.
I’m not talking about new laws of physics. I’m just saying we may get so good at moving around our own system and utilizing the mass in our system that we never need to go anywhere else other than for pure exploration. And it may be so freakishly hard to move between the stars that we never get a cost-benefit high enough for us to do it. It might be that we would use up so many resources and so much energy trying to expand outwards that it never makes sense.
For example, Let’s say our probe can be made for 1,000kg, and we want to send it at 1/3 the speed of light. The kinetic energy of that probe would be 12,054 TWh, or roughly the same as all the energy used on Earth in a year. Double it because we have to slow down at rhe other end. And 1,000kg for a probe that has to explore another star system, find materials, mine them, smelt them, and manufacture them into a copy of itself is ridiculously low. If it had to be 100 times that size, we’re talking about two century’s worth of Earth’s energy consumption for one probe. And even that’s probably way too small, given that 90% of the launch mass will be fuel (assuming a fusion drive, but no new science like wormhole drives or whatever). It is insanely expensive in energy to send real mass to other stars. And it may be that the interstellar environment is so hostile that 90% of high speed probes never make it between stars.
If you can do more with that energy in your own system, there’s no need to go elsewhere.
Sure. The point I’m making is that we are making some fairly strong claims about aliens based on what we know, but what we know may be so insignificant that any ‘answer’ to the Fermi paradox might as well be a shrug. So long as everyone understands that any statement about the likelihood of other civilizations should come with error bars so large that just about any conclusion can fit within them.
The whole point to the Drake equation is to reduce those error bars so we can start testing various hypotheses, but we are nowhere near that yet. There are still reasonable ‘solutions’ to the Drake equation which show millions of likely civilizations, and other solutions that make life so wildly unlikely that our own existence is incredibly lucky. Both fit our current data.
Even the ‘where are they’ question can be answered, “Who’s to say they aren’t all over the place?” Our ability to detect other civilizations is still close to zero. If someone on a planet around the closest star to us was transmitting radio at the same power levels we do, the same way we do, we would not have detected it.
To date, we have had almost no ability to look for life signs on planets around other stars. Hell, we thought we might have discovered a Dyson sphere around ‘Tabby’s star’, which is in our galactic backyard, but it turned out to be a dust cloud. Had it been a Dyson sphere, it would have been right there for decades of telescopic observations and we didn’t know it. There could be a thousand Dyson sheres in pur galaxy right now, waiting to be discovered. There could be million civilizations at our level scattered through the galaxy and we’d have no way to know.
That is all fine speculation, so don’t take this as me saying you’re “wrong”.
But my position is still that these problems are hard to us but unlikely to remain hard for thousands of years, let alone millions.
In terms of the energy required, we know for a fact humans have not scratched the surface of energies available. A fusion device would tap orders of magnitude more energy than all of our history combined and that’s just assuming it could only use hydrogen, from earth, say. But, IIRC, any nucleus lighter than iron can fuse and liberate energy. So essentially almost all of the matter of any celestial object.
Regarding carrying fuel, we already know numerous ways to launch objects without them carrying their own fuel. Solar sails, slingshots, or heck, just being towed. For us right now we tend to make vehicles that carry their own fuel just because that works best for trying to get things out of our gravity well. But even we jettison parts of the vehicle in stages.
It would take 120 days to accelerate to 1/3 light speed at 1g of acceleration. Make it 240 days so you can slow down.
2-3 grams of antimatter is sufficient to orbit the space shuttle. Let’s say 100x that much for an intrestellar space ship. Say 300 grams * 2 (slow down) = 600 grams * 240 days = 144,000 grams. Or, 144 kilos.
You can fiddle with the numbers as you like but it would seem possible to have a reasonable amount of fuel on a spaceship to make such a trip.
And yeah, I know antimatter is super rare today and expensive doesn’t begin to cover it. Just a thought experiment.
The big problem with an antimatter drive is that it is too powerful, and most of the energy is released as gamma-rays. Gamma-rays would pass through a lot of shielding, and would be dangerous to the payload and passengers, and would also be challenging to convert into thrust. Many antimatter reactions produce a lot of neutrinos too, which are far too insubstantial to be converted to thrust. We also have to consider the waste heat from such a powerful engine, which would melt the ship unless you include vast radiative surfaces.
One solution to the dangerous nature of an antimatter drive was suggested by Robert Frisbee; put the passengers and crew a long way away from the drive. Like 700km away. This implies a very long, and very massive, ship, which would require very, very large amounts of antimatter.
Antimatter propulsion is a conundrum that hasn’t yet got a good solution.
A gram of antimatter, when fully annihilated with a gram of regular matter, produces 1.8x10^14J of energy. The kinetic energy required to accelerate 1,000kg to .3C is 4.34 X 10^18 J if I did my math right.
That means you’d need about 160,000 kg of matter and antimatter for your 1,000kg probe, assuming 100% efficiency. But of course, you need to slow down, so you need to carry 160,000kg of antimatter as payload, which means the total amount you would need is millions of kilos. The rocket equation is a bitch.
As a sanity check, here is a paper that looks at a 4-stage beamed propulasion matter/antimatter starship and has this comment:
That’s a fuel-to-payload ratio of 400,000:1.
And 100 tons is a very small probe. For comparison, the ISS weighs 450 tons.
Interstellar travel is hard - much harder than even most enthusiasts think. And whatever is at the destination better be more valuable than 40 million tons of antimatter, or you aren’t going to bother to make the trip. As a reference, a microgram of antimatter today is worth $60 billion or so.
Which brings me to another ‘great filter’ - what are the odds that a civilization that can manufacture millions of tons of antimatter wouldn’t blow itself to smithereens first? A gram of antimatter has about the same energy as a 20 kiloton nuclear bomb. A kilogram would be 20 megatons, about the size of ‘Tsar Bomba’, the biggest fusion bomb we’ve ever detonated. A ton of antimatter is equivalent to 1,000 of the biggest fusion bombs we ever detonated. Detonating 40 million tons of the stuff would be…bad.
160,000 only if you don’t want to slow down at the other end. If you do, 40 million tons is closer. And that’s for a measly 100 ton probe, which you point out is 1/20 the mass of a space shuttle.
We need a probe that is not only going to slow down, but to be able to manoever around a distant system on its own, land on planets and/or moons, explore for, mine and refine numerous materials, build manufacturing facilities AND make another 40 million tons of fuel for the replicated probe. You think a 100 ton probe is likely to do that?
It shot them into space, not into orbit. Huge difference. The point remains that the people in the 1800’s who thought we would inevitably shoot people into space when cannon tech got there were wrong, because long before we have that tech we already had a better way. The space elevator may suffer the same fate, being obsoleted before it ever becomes feasible.
There is no evidence of that. Some problems may simply be intractable, or cost so much energy that they don’t make sense.
When I was young, lots of ‘futurists’ extrapolated curves of maximum attained velocity and other rapidly-improving metrics and assumed we would be travelling relativistically by now and living in space colonies. In reality, we stopped going faster very shortly thereafter, and progress in space flatlined. Even our airplanes got slower. As they say, past performance is no guarantee of future results.
For all we know, we are already reaching practical limits that won’t be exceeded for centuries, or ever. Maybe fission rockets are the absolute best we ever manage, and we’ll never go faster than a tiny fraction of the speed of light, ever.
We just went through a century-long burst of technological evolution. There is no law that says that has to continue. Maybe after you pick the low hanging fruit the pace of innovation slows to a crawl. We’re making 5 nm ICs now - we could be getting close to the theoretical minimum size and progress in digital circuits will stall out. We really don’t know.
But it’s crazy to assume that as long as a civilization is old enough it will ‘solve’ easy interstellar transport. There are fundamental reasons to believe that might not be the case.
Not only have I said this myself, but I put it in bold because I know how this discussion often goes.
Yes, even advanced ETs will be limited by the laws of physics.
Let’s put it this way. Let’s put all known problems related to space travel in two buckets: tractable and intractable.
Now, when it comes to a species millions of years of technological progress ahead of us, my personal opinion is that many of the things in the “intractable” bucket may turn out to be tractable after all. But, we can put this to one side as it’s irrelevant to the discussion.
Because, all I am saying in this discussion is that the things in our tractable bucket are likely to be trivial by that point in time. Making self-replicating drones, to us, looks nightmarishly difficult, but not physically impossible and therefore: tractable.
We’re talking about a species that is thousands of times further ahead of us than we are ahead of cave men. “It looks hard to engineer” just isn’t going to cut it as a Fermi solution.
I missed this earlier. It’s not clear that a space elevator will be more fuel efficient, because space elevators are massive and have to be launched into space, and then will have a finite lifespan to recoup that sunk cost before being decommissioned.
And who cares about fuel? Fuel can be manufactured. In the case of methane, it can even be manufactured to be carbon-neutral. So it comes down to cost. Musk says Starship can eventually get mass to orbit for $10/kilo. Even if that is ‘aspirational’ it seems likely that we’ll eventually get close to it. How much does a space elevator cost, and how long will it last? What does it cost to operate per year, and how much mass can it move in a year? Those numbers will determine if it’s competitive with reusable rockets. At first blush, I think that would be very hard to achieve.
Another issue is that a space elevator can only deliver payloads to GEO and over one specific place over the Earth, but the vast demand is for LEO satellites, and even the GEO ones will have to carry fuel to move them into the correct orbit.
We also have no evidence that a technological civilization can be maintained for millions of years. Perhaps they are fundamentally unstable, or they go through regular periods of reset and rebirth. Look how many civilizations we’ve gone through just in a few thousand years.
Sure, but that isn’t so relevant to the topic of reproducing probes, which do appear to be something that will be feasible within the next millenia.
In more general terms regarding the Fermi paradox, even if civilizations are fragile, the issue is that once a species can spread beyond its homeworld (and in this case, we don’t just meet spreading to other planets, but to any kind of colony e.g. generation starships) it’s more a question of how long civilizations survive relative to the time to set up the next colony.
1000 light-years is a ludicrous, ridiculous distance.
However, it is not so far for it to rule out any communication or contact, far from it. Indeed a species that has no interest in exploration, but just built an object that emitted a great deal of EM radiation would be seen by us…a thousand years later. A minute fraction of the age of the universe or galaxy.
Communication? Perhaps a one way "we are here’ type of thing. like we sent out, sure. But by the time we get it, who is to say that the civilization that sent it is still extant?
But no visits or close encounters or space invasions.
Thus your original point seems to have been refuted. You said “[no sentient intelligence] can possible be close enough for us ever to know about it”.
What is your basis for any of this? It’s a crazy far distance, as I say, but we are not aware of any physical limitation that rules out any of these things.